1. Field of the Invention
This invention relates to novel liquid crystal devices comprising a lyotropic-type cholesteric liquid crystal. The lyotropic-type cholesteric liquid crystal is a concentrated solution of a cellulose ether or ester, as specified below, in water or an organic solvent.
2. Description of the Prior Art
Liquid crystal devices comprising a lyotropic-type cholesteric liquid crystal are well known. Such devices are of a structure such that the liquid crystal is surrounded by an enclosure. At least a part of the enclosure is transparent, so that the color of the liquid crystal varies depending on the change of environmental conditions, such as temperature, types of electric fields and pressures, and the like. Most cholesteric liquid crystals used are esters of cholesteric compounds such as cholesteric derivatives, e.g. cholesteric carboxylates and carbonates of cholesteric alcohol. These liquid crystals are capable of selectively reflecting the incident light and of exhibiting color variation effects depending upon the change in environmental conditions such as temperature, types of electric fields and pressures. However, most of these liquid crystals are not stable against exposure to ultraviolet radiation and heat.
Lyotropic-type liquid crystals comprised of alkali salts of an aliphatic acid, anionic surfactant and high polymeric substances are also known. However, no liquid crystal devices comprising these materials have been heretofore proposed for use for color variation effects.